I'm in the process of coding up a piece of middleware to take information from our wireless lan controller and pass it up to our web filter. I'm currently a bit stuck because the WLC syslog contains user names and MAC addresses but no IP addresses.

How can I quickly turn MAC addresses into IP addresses so that I can pass which username belongs to which IP up to the web filter?

This script runs on a Debian Linux box so I'm happy to hand the MAC off to an external program. I had considered using arping but concluded that would likely be too slow.